1. Field of Invention
The present invention relates to a high voltage device and a manufacturing method thereof, in particular to such device with an enhanced breakdown voltage and a method for manufacturing the device, in which the high voltage device and the low voltage device can be manufactured by common manufacturing process steps.
2. Description of Related Art
FIGS. 1A and 1B respectively show a cross-section view and a 3D (3-dimensional) view of a prior art double diffused drain metal oxide semiconductor (DDDMOS) device which is manufactured by the following steps: as shown in FIGS. 1A and 1B, forming an isolation structure 12 in a P-type substrate 11 to define a device region 100, wherein the isolation structure 12 is, for example, a shallow trench isolation (STI) structure or a local oxidation of silicon (LOCOS) structure; and forming a gate 13, a source 14, a drain 15 and a drift region 16 in the first device region 100. The drift region 16, the drain 15 and the source 14 are formed by a lithography process and an ion implantation process, wherein the lithography process defines the implantation regions by a photoresist mask together with a self-alignment effect provided by all or a part of the gate 13 and the isolation region 12, and the ion implantation process implants N-type impurities to the drift region 16, the drain 15 and the source 14. The drain 15 and the source 14 are at different sides of the gate 13 respectively, and the drift region 16 partially interfaces with the bottom surface of the gate 13 at a side of the gate 13 closer to the drain 15 than the source 14. The DDDMOS device is a high voltage device designed for applications requiring higher operation voltages. However, if it is required for the DDDMOS device to be integrated with a low voltage device in one substrate, the high voltage device and the low voltage device should adopt the same manufacturing process steps with the same ion-implantation parameters, and thus the flexibility of the ion-implantation parameters for the DDDMOS device is limited; as a result, the DDDMOS device has a lower breakdown voltage and a limited application range. To increase the breakdown voltage of the DDDMOS device, additional manufacturing process steps are required, that is, other lithography process and ion implantation process are required in order to provide different ion-implantation parameters, but this increases to cost.
In view of above, to overcome the drawbacks in the prior art, the present invention proposes a high voltage device and a manufacturing method thereof which provide a higher breakdown voltage and a broader application range for the high voltage device, in which additional manufacturing process steps are not required such that the high voltage device and the low voltage device can be manufactured by common manufacturing process steps.